Role of Adiponectin Receptor 1 in Promoting Nitric Oxide-Mediated Flow-Induced Dilation in the Human Microvasculature

FIGURE 1. AdipoR1 expression in human microvessels. Representative images showing expression of CD31 (green) and AdipoR1 (red) in arterioles from patients without CAD (A), with CAD (B) and arterioles treated with siAdipoR1 (C). CD31 was used to identify the endothelium to allow for measurement of AdipoR1 in the intimal layer of the vessel. (D) Measured relative intensity of AdipoR1 in all groups. (n = 3 for nonCAD and CAD, n = 4 for vessels treated with siAdipoR1; 3 nonCAD, 1 CAD), *p < 0.05).

FIGURE 2. Adiponectin restores NO-dependent FID via activation of AdipoR1 in CAD microvessels. (A) FID is significantly decreased in arterioles collected from patients with CAD treated with both siAdipoR1 and adiponectin in the presence of PEG-catalase (n = 5) compared to vessels treated with siAdipoR1 alone (n = 5) whereas L-Name had no effect (n = 4). (B) Intraluminal treatment with negative control siRNA does not impair adiponectin-induced restoration of NO as the mediator of FID as dilation is inhibited in the presence of L-NAME (n = 4) compared to negative control siRNA alone (n = 5). ‡ p < 0.01, *p < 0.05 versus AdipoR1 siRNA alone. n indicates the number of patients.

FIGURE 3. Role of AdipoR1 in FID within the human microvasculature. (A) FID in nonCAD arterioles with reduced expression of AdipoR1 was significantly impaired in the presence of PEG-catalase (n = 4) compared to siAdipoR1 alone (n = 4, ‡ p < 0.01) whereas L-NAME had no effect (n = 5). (B) Dilation to flow in arterioles from CAD subjects treated with siAdipoR1 and PEG-Catalase (n = 5) was significantly decreased compared to vessels treated with siAdipoR1 alone (n = 6, ‡ p < 0.01), however L-Name had no effect (n = 4).

FIGURE 4. Osmotin as potential activator of AdipoR1. (A) FID in CAD arterioles treated with osmotin (0.3 μM, 16–20 h) was not reduced in the presence of the NO scavenger cPTIO (n = 4) or PEG-catalase (n = 5). Significant reduction of maximal dilation was only observed with both inhibitors (n = 3, *p < 0.05). (B) The effect of osmotin was eliminated in arterioles from CAD patients with reduced expression of AdipoR1 as PEG-catalase significantly decreased overall dilation (n = 4) compared to siAdipoR1 and osmotin (n = 5, ‡ p < 0.01) whereas L-Name had no effect (n = 4). (C) The primary mediator of FID remains dependent on H2O2 despite osmotin treatment in arterioles treated with negative control siRNA (n = 5 for both PEG-catalase treated and no inhibitor, ‡ p < 0.01) as opposed to NO (n = 7; L-Name).

FIGURE 5. AdipoR1 signaling in the microvascular endothelium. Activation of AdipoR1 by adiponectin (blue) can activate multiple downstream pathways including AMPK and PI3K via the adapter protein APPL1. Adiponectin receptors have intrinsic ceramidase activity that allows for hydrolysis of ceramide to sphingosine. Exogenous adiponectin promotes NO-mediated FID in vessels from patients with CAD while accumulation of ceramide in healthy vessels promotes formation of H2O2 during flow. Osmotin (purple) like adiponectin activates AdipoR1, APPL1, AMPK, and PI3K however dilation to both NO and H2O2 is observed in arterioles from subjects with disease. Whether osmotin is capable of triggering the ceramidase activity in AdipoR1 remains unknown. *ceramidase activity is within the adiponectin receptor.